1. Field of the Invention
This invention relates to a heat fixing device for electrographic apparatus or the like.
2. Description of the Prior Art
Various kinds of electrographic apparatuses have been proposed and used in practice.
In a conventional electrographic apparatus, a photosensitive drum coated thereon with a photoconductor such as Se, ZnO or the like is rotated, charged with a corona source of ions, exposed, the charge image developed, the developed image transferred to a record sheet, and finally the toner image is fixed, generally by fusing. After the transfer operation, the residual image is erased from the surface of the photoconductor and the photoconductor is cleaned in preparation of a repetition of the process.
In the above described electrographic apparatus, the heat fixing device is provided with a pair of opposed guide members spaced apart from each other to form a record sheet feeding path and a pair of opposed supply sources spaced apart from each other to include therebetween the guide members. Alternatively, one heat supply source only may be opposed to the toner image transferred to the record sheet. The guide members and heat supply sources are supported by a supporting frame of the electrographic apparatus.
As the heat supply source, use may be made of a nichrome heater, halogen lamp, infrared lamp or the like. The guide members may generally be formed of a metal plate, metal wire with or without coated with an insulating substance.
In such kind of heat fixing device, the metal guide member is connected directly or through the metal supporting frame to ground. As a result, if the record sheet with the toner image transferred thereon reaches between the guide members, an electric attractive force is applied between the record sheet and one of the guide members and the record sheet is easily brought into contact with the guide member. The more the amount of the toner particles adhered to the record sheet the stronger the electrical attractive force.
Particularly, if the toner image side of the record sheet makes contact with the guide member, the toned image is rubbed with the guide member to disturb the picture image. If the record sheet is adhered to the guide member by the adhesive property of the toner particles, there is a risk of the record sheet being clogged and eventually being burnt.
If the guide member is formed of a heat resistant insulating material, the electric attractive force thereof can be made small. But, it is very difficult to provide a guide member which has an excellent guiding action along a relatively long feeding path and which is less expensive and has an excellent heat resistant insulating property.